Lateral parabrachial serotonergic mechanisms: angiotensin-induced pressor and drinking responses.

This study investigated the effects of bilateral injections of serotonergic receptor ligands into the lateral parabrachial nucleus (LPBN) on the pressor and dipsogenic responses induced by intracerebroventricular (i.c.v.) injection of angiotensin II (ANG II). Rats with stainless steel cannulas implanted bilaterally into the LPBN and into the left lateral ventricle were used to study i.c.v. ANG II-induced water intake and pressor responses. Pretreatment with the serotonergic 5-HT1/5-HT2 receptor antagonist methysergide (1-8 micrograms/200 nl) bilaterally injected into the LPBN increased the water intake induced by i.c.v. ANG II (50 ng/microliters) administered via the lateral ventricle, but pretreatment with methysergide (4 micrograms/200 nl) did not change the pressor response produced by i.c.v. ANG II. After bilateral injection of either serotonin (5-HT, 5 micrograms/200 nl) or the serotonergic 5-HT2a/5-HT2c receptor agonist (+/-)-2,5-dimetoxy-4-iodoamphetamine hydrochloride (DOI; 0.5-10 micrograms/200 nl) into the LPBN, the water intake induced by ANG II was significantly reduced. These results are consistent with Other observations indicating that the LPBN is associated with inhibitory mechanisms controlling water intake induced by ANG II treatment and suggest that serotonergic pathways may be involved in this effect.